a) Field of the Invention
The present invention relates to several improvements to the basic structure of a scaffolding hereinafter called “platform assembly”, which is designed to be self-standing or to be erected close to a building wall in order to help workmen to construct, repair or otherwise work on this wall.
More specifically, the invention relates to improvements made to a self-raising platform assembly comprising at least one mast along which a platform may be moved up or down by means of a lifting mechanism including a hydraulically operated ram extendable and retractable along the mast. The so-made improvements lie in particular in:                the structure of the base of the mast(s);        the structure of the mast(s);        the structure and operation of the lifting mechanism;        the way the platform is guided along the tower(s); and        the structure of the platform itself.        
b) Brief Description of the Prior Art
Platform assemblies made of modular elements that can be erected close to a building structure so those workmen can work on the same, are well known and commonly used in the construction area.
As non-restrictive examples of such assemblies, reference can be made to U.S. Pat. No. 3,323,616 (BEST) and U.S. Pat. No. 5,159,993 (ST-GERMAIN A.) which disclose platform assemblies wherein the platform are moved by a cable hoist mechanism.
Reference can also be made to U.S. Pat. No. 4,809,814 (ST-GERMAIN J.) which discloses a platform assembly wherein the platform is moved by a set of hydraulically operated rams and hooks devised and positioned to engage steps made in the masts in order to lift up the platform.
Reference can further be made to U.S. Pat. No. 4,293,054 (PIERI) and U.S. Pat. No. 4,294,332 (READY) which disclose platform assemblies comprising two masts along which a working platform may be moved up and down by means of toothed wheels that are driven by an electric motor through a suitable transmission. The toothed wheels are meshed with corresponding gear racks mounted on bars forming part of the masts.
Reference can finally be made to U.S. Pat. No. 5,579,865 (BUTLER et al) which also discloses a platform assembly of the above mentioned type, having a platform whose length and/or width may be adjusted by addition of modular platform segments.
If all these existing platform assemblies are quite efficient, they still need to be improved in numerous ways, especially in terms of structures and operation of its basic components which, to make the platform assembly interesting in use, must be strong, safe, reliable, easy to assemble and preferably modular.